The present invention relates to positive-displacement fluid pumps, such as a rotary gear pumps and rotary vane pumps. In particular, the present invention relates to protective coatings for use in positive-displacement fluid pumps.
Positive-displacement fluid pumps are fluid transfer equipment employed in a variety of industrial and commercial systems for pumping fluids from one location to another. For example, positive-displacement fluid pumps may be used in aircraft to pump fuel from storage reservoirs to turbine engines during flight. Such pumps typically include rotary components (e.g., rotatable gears) that rotate within a housing to transfer the fluids. To increase pumping efficiencies, the rotary components are retained as close as reasonably possible to the housing to reduce leaks. However, this can induce abrasive or adhesive wearing of the rotary components and the housings during the course of operation.
One technique for reducing the rate of wearing includes the use of side or end plates composed of monolithic-cemented carbide or case-hardened steel. The side and end plates are correspondingly subjected to wear, thereby reducing damage to the rotary components and the housings. However, such materials can increase frictional resistance between the rotary components and the housing, which can reduce pumping efficiencies, and potentially cause metal-to-metal seizures.
Another option includes the use of side or end plates having steel or aluminum substrates coated with a leaded-bronze, sacrificial material (or the plates are solid leaded-bronze). The lead in the sacrificial material is capable of smearing around the steel substrate rather than being worn down. However, because of potential environmental and health concerns associated with the manufacture and use of lead, leaded-bronze materials are falling into disfavor. As such, there is a need for a protective coating that avoids the potential health concerns associated with lead-containing materials, but retains the positive properties of leaded-bronze materials.